The prevention of ice-formation and slipperiness is extremely important at airports in order to maintain safe conditions for take-off and landing as well as for general aviation safety. The most important requirement for the anti-skid treatment at airports is ensuring aviation safety by maintaining sufficient friction on the asphalt surface of the runway. There is a certain friction requirement for runway paving, and this must be fulfilled whenever there is air traffic at the airport. The coefficient of friction is a constant that describes the interface between two solid substances, and it expresses the amount of friction present as the bodies slide against each other. The coefficient of friction is always more than zero and in practice always less than one. As far as the friction requirement at airports is concerned, the value must usually be at least 0.3, preferably 0.4.
Mechanical methods are primarily used for anti-skid treatment on runways. Chemical melting agents are required for removing the hoarfrost and ice formed on the runway surface, as well as for anticipatory anti-skid treatment. In general, ice-melting agents are used for the anti-skid treatment, optionally with added thickeners in order to increase viscosity, as well as water, surfactants and corrosion inhibitors. The purpose of the ice-melting and anti-skid agents is to disrupt and weaken the adhesion of the ice to the surface of pavement, after which the surface can more easily be mechanically cleaned.
For the prevention of slipperiness on roads, chlorides have mainly been used as ice-melting and anti-skid agents. The substances that are used in road maintenance, such as sodium chloride, could not be used at airports, since they rapidly rust and erode the metal parts of the planes as well as airport equipment. In addition, chlorides have a harmful effect on groundwater quality, soil, vegetation and soil microfauna. Traditionally, water-soluble organic compounds such as urea have been used for melting ice at airports. However, the use of urea has largely been given up, since it has been found to cause significant environmental damage, especially due to nitrogen's eutrophicating effect. As a result of the use of urea, oxygen depletion may occur in groundwaters, increasing the dissolution rate of heavy metals. At present, acetates, liquid potassium acetate and solid sodium acetate, as well as formates, potassium formate and sodium formate, are used at airports. In comparison to chlorides and urea, acetates and formates are less detrimental to the environment. Acetates and formates are effective in melting ice, but their drawback comprises the heavy corrosion of metals and electrical equipment. After the introduction of ice-melting agents based on acetate and formate, issues with asphalt pavements have been observed at airports. What is also significant in relation to the present invention is the fact that ice-melting agents based on acetate and formate have been found to cause heavy corrosion in aeroplane materials, including carbon fibre brakes, metal surfaces and mating metal-metal surfaces. All these issues caused by nominal deicing agents increase the risk of aviation safety.
In anticipatory slipperiness prevention, liquid ice-melting agent has been found to be the most usable form of an ice-melting agent, since a solid and often granular ice-melting agent is easily carried away from the intended surface under the influence of air flows. Further, the effect of granular ice-melting agent is very local, and therefore the effect starts fairly slowly and the applied amount is substantially higher than when a liquid or wetted substance is used. Liquid ice-melting agent is more easily distributed over the entire surface, thus covering a substantially larger proportion of the pavement surface than a solid substance. Previously, liquid substances comprising about 50% water have usually been used for the removal of hoarfrost and thin ice. To remove thicker ice, granular substances are required, which melt the ice down to the surface of the runway if necessary, after which the surface is cleaned by snowploughing or brushing. At present, liquid substances are mainly used (nearly 80% of all substances used) for the anti-skid treatment at airports, since a thick layer of ice is rarely allowed to form on the runway.
As a result of better understanding, environmental considerations and especially the accumulation of chemicals and their effect on the environment have gained increased significance. Especially in view of the environmental considerations concerning the former ice-melting agents, there is a great need for developing novel ice-melting agents that possess the efficacy necessary in the prevention of slipperiness.
EP 1034231 discloses a composition for anti-skid treatment in which aqueous solution comprising 10-60% betaine or its derivatives is used as an anti-freezing agent for runways and as an anti-skid agent for runways.
U.S. Pat. No. 6,596,189 discloses a liquid-based anti-freezing composition for airport runways, the composition exhibiting a minimal catalytic oxidative effect on carbon-carbon fibre composite brakes. This composition comprises mixtures of alkali and alkali earth metal carboxylates and alcohols, into which additional corrosion inhibitors have been added.